The invention concerns a method of operating the closing means of a double plate injection moulding machine including a fixed and a movable mould plate, the closing means comprising at least one pump, at least one high speed cylinder for a high speed stroke and at least one closing cylinder for a high power stroke with a nominal closing force, whereby the closing cylinder includes a double action piston in which both piston faces are the same size and which divides the interior of the closing cylinder into two cylinder sections which are hydraulically connectable via hydraulic lines and a valve.
Closing means for double plate injection moulding machines normally have independently operable piston cylinders to carry out a high speed stroke and a high power stroke.
In conventional methods for operating such closing means, firstly the mould half which is fixed to the movable mould plate is quickly urged towards the mould half which is fixed on the fixed mould plate by means of the high speed cylinder, using a small closing force. Then the two mould halves are closed or held together by the high hydraulic pressure which has been built up in the high power cylinder. The injection operation is then carried out (including the pressure dwell phase). Following a cooling phase after the injection operation, the mould halves are opened by completely releasing the hydraulic pressure from the high power cylinder, and the injection moulded article is removed from the mould. This completes a machine cycle and the next machine cycle is begun by closing the two mould halves once again.